In one shot of the Charicific Valley flashback, Ash's left sleeve is colored blue like the rest of his jacket instead of white.
As the view zooms in on Charizard's Poké Ball after Ash receives it, the cuff of his glove is colored green like the ones he used in Hoenn and Sinnoh.
Before Professor Oak and Ash exchange Charizard for Unfezant, Oak's eyes are brown instead of black.